This invention relates to strength testing of ceramic honeycomb structures. More particularly, the invention relates to apparatus and methods for testing the compressive strength of such structures.
Compressive strength is an important feature of thin-walled ceramic honeycomb structures, which are used in the manufacture catalyst supports. Honeycomb structures have a webbed cellular or channeled core structure surrounded in most cases by a smooth integral outer skin layer. The manufacture of structures by extrusion to form cellular ceramic honeycombs of cordierite composition and very low thermal expansion from plasticized mixtures of ceramic batch materials is described in U.S. Pat. Nos. 3,790,654 and 3,885,977. Such honeycombs remain in widespread commercial use as catalyst supports for emissions control applications such as automotive exhaust treatment systems.
One way of improving the exhaust conversion efficiency of catalyst supports is to produce honeycomb products with thinner webs. Currently, the assignee of the present patent application manufactures catalyst supports having web thicknesses in the range of two mils. Thinner webbed structures result in parts that have reduced compressive strength. In the manufacture of exhaust system components, catalyst supports are typically surrounded with a housing comprised of a metal layer. The process for surrounding the parts with a metal layer is known in the art as xe2x80x9ccanningxe2x80x9d. The canning process used to place a metal housing around ceramic catalyst supports exerts compressive stresses on the catalyst support. Manufacturers of catalyst supports must be able to provide products that are able to withstand compressive forces encountered during canning processes.
Various apparatus exist for testing compressive strength of ceramic honeycomb structures. One type of apparatus involves enveloping a sample in a rubber boot, immersing the enveloped sample in hydraulic oil and applying isostatic pressure to the sample from all directions. One drawback of this apparatus is that it does not simulate the true compressive forces encountered by catalyst supports during the canning operation. Furthermore, this type of apparatus is relatively large and stationary. In addition, the envelopment, loading and removal of the sample is time consuming, inconvenient for the operator and unclean because the enveloped sample is loaded directly into the hydraulic oil. Since the apparatus is too large to transport, samples must carried to and from the machine. Various apparatus exist for testing tubular products, however, these apparatus do not permit rapid loading, testing and unloading of the product. New methods of testing ceramic honeycomb structures, particularly in a production environment, are needed.
The invention relates to apparatus and methods for testing the compressive strength of ceramic honeycomb structures. In certain embodiments, a portable compressive strength testing apparatus is provided. According to other embodiments, samples can be easily and rapidly loaded, tested and unloaded from the apparatus. In some embodiments, the portability of the apparatus and the ease and speed of loading, testing and unloading samples facilitates the testing of large quantities of ceramic honeycomb structures. In other embodiments, a failure detector is provided to determine when a part has experienced failure that cannot be detected by visual inspection.
Advantages of the invention will be apparent from the following detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed.